There was no indication that the downing of the airliner, which killed all 176 people aboard, was due to a cyberattack on Iran's missile or air defense systems, Torki said, adding that three people were under arrest related to the accident.
The airliner was shot down shortly after takeoff in Tehran, when Iran's air defenses were on high alert, hours after Iran had fired missiles at a US base in Iraq in retaliation for the assassination of Iranian Lieutenant General Qassem Soleimani, commander of Islamic Revolution Guards Corps’ Quds Force.
"The portable system which fired the missile did not accurately determine the real north after rebooting, and this huge mistake caused the operator of the air defense system to see the plane on its radar as a target that is approaching Tehran from the northwestern region," Torki said.
He added that the operator of the air defense system notified the target to the relevant coordination center, but did not receive a response.
"Unfortunately, the operator fired while the connection was disconnected only for a few seconds," he said.
"The biggest mistake was that the system fired without receiving permission from the network," he stressed.
Torki said that the people who have been made the mistakes have been arrested.
Torki added that the black boxes of the airliner have been physically damaged and reading them is technically complicated.
Iranian Deputy Foreign Minister Mohsen Baharvand said on Sunday that decoding the black boxes of the Ukrainian plane will begin on July 20.
France's BEA crash investigation agency also said on Friday it would download the black boxes from the airliner at Iran's request.
Mehr News Agency and Reuters contributed to this story.